The practice of water baptism has its roots in the Jewish rite of purification.  Today that practice is performed by immersion in a specially constructed pool known as a "mikvah." 

In Temple times, the priests as well as each Jew who wished entry into the House of G-d had first to immerse in a mikvah.

In many ways mikvah is the threshold separating the unholy from the holy, but it is even more. Simply put, immersion in a mikvah signals a change in status -- more correctly, an elevation in status. Its unparalleled function lies in its power of transformation, its ability to effect metamorphosis.  (The Jewish Woman, The Mikvah, chabad.org)

The Mikvah is a special part of the ceremony observed in the conversion of a Gentile to Judaism.

Men or women in Temple times, who were precluded from services because of ritual defilement, could, after immersion, alight the Temple Mount, enter the House of G-d and involve themselves in sacrificial offerings and the like. The case of the convert is most dramatic. The individual who descends into the mikvah as a gentile emerges from beneath its waters as a Jew.  (Gateway to Purity, Rebbetzin Rivkah Slonim, www.torah.org)

Thus, total immersion is the mode of water purification normally practiced in Judaism today.  The one exception is with a deceased person where pouring rather than total immersion is practiced:

The mikvah concept is also the focal point of the taharah, the purification rite of a Jew before the person is laid to rest and the soul ascends on high. The manual pouring of water in a highly specific manner over the entire body of the deceased serves this purpose.  (The Jewish Woman, The Mikvah, chabad.org)

, Thayer's Greek-English Lexicon states:

Baptizo...to dip repeatedly, to immerge, submerge.  2. to cleanse by dipping or submerging, to wash, to make clean with water

Burial.  The Noun:  1. entaphiasmos, lit., an entombing (from en, in, taphos, a tomb),

                                2. taphe, a burial (place) (An Expository Dictionary of New Testament Words, W. E. Vine)

The idea of burial is to remove an already dead body from the sphere of living people.  Circumcision (Col. 2:11), like crucifixion, is the cutting off (death).  Burial is the removal of that dead body from possibility of contact with the living.  Baptism (Rom. 6:4; Col. 2:12) is likened to burial.  The person baptized is dead.  Baptism is not a 'testimony' of one's faith in Christ, or a 'witness' to one's salvation.  Thus, baptism was a ceremonial washing away (removal, cleansing) of sins in an earthly setting.  Clerical Judaism, and those connected with it, had crucified the Lord.  Baptism left all that behind.  Baptism had nothing to do with heaven, Christ's vicarious atonement has to do with it. Baptism was done in a governmental setting (on earth).  It symbolized the fact that one who was of the first man Adam, the dead man, was forever left behind, entombed, buried, in favor of a new sphere of blessing in the new creation. 

Burial can be in the ground ("six feet under"), or in a tomb.  Lazarus, and the Lord Jesus were both buried in a tomb.

In patriarchal times, successive generations were buried in cave or rock-cut family tombs: Sarah, Abraham, Isaac, Rebekah, Leah and Jacob were all buried in a cave at Machpelah.

When Israel was in Palestine, the practice of burial in ancestral tombs was continued when possible.  Tombs were usually outside the town; land was set aside outside Jerusalem for 'the graves of the common people' (2 Ki. 23:6).

David's tomb was remembered in NT times (Acts 2:29).

Graves of criminals or enemies were sometimes marked with a heap of stones (Jos. 7:26); cremation was not a normal Hebrew practice.  (New Concise Bible Dictionary, Editor: Derek Williams, Inter-Varsity Press)